In a number of circumstances it is desirable to be able to monitor muscle activities of especially human beings, in particular with the objective of being able to detect and possibly avoid undesirable, unnecessary and/or potentially harmful muscle activities. In particular it is desirable to be able to detect such muscle activities with the objective of being able to interfere in such a manner that the undesirable activity may be limited or even brought to an end.
Examples of such situations are for example work situations where muscles are used incorrectly whereby irritation, pain or even damage may occur. This also relates to circumstances where muscles are strained during work stress and/or where person suffer from pain in the back of the head and shoulder caused by incorrect work position. Examples of this may be monotonous work (RSI—Repetitive Strain Injury; CTD—Cumulative Trauma Disorders; CTS—Carpal Tunnel Syndrome), work at a PC-station, (e.g. computer mouse overuse syndrome), office work (incorrect sitting) etc.
Also muscle activities may be concerned, which are brought about more or less consciously or even completely unaware, for example in the sleep, and which may also cause damage or unwanted effects.
As an example of such undesired muscular activities reference may be made to the affliction bruxism that in general is defined as powerful jaw movements without any real function and which takes the form of involuntary grinding movements of the teeth during strong clenching. This affliction may cause serious dental damages such as for example wearing of the teeth, damages to lips and the tongue, lose teeth, gingival pockets etc. Bruxism is often in addition also associated with pain in the back of the head and chronic headache.
Bruxism is normally divided into chronic and acute bruxism. Acute bruxism can happen to all and may often be observed in stress situations, for example at athletes in games or at persons that have to observe a deadline. Chronic bruxism is divided into nocturnal and daytime bruxism. Daytime bruxism is characterized by being a conscious clenching of upper and lower jaws and grinding of the teeth, although dominated by the latter. Since night-time bruxism is unconscious it may normally only be perceived by the surroundings (for example relations) as an unpleasant squeaky noise. The daytime bruxism may often be provoked by exposing the patient to stress. This daytime bruxism may be perceived as a bad habit. This form of the affliction may be relieved relatively easy by drawing the attention of the person to the bruxism. As regards night-time bruxism the problem is more complex since it is difficult to distinguish between bruxism events and ordinary muscle activity. It is noted, though, that bruxism typically lasts more than 2-5 seconds. This nocturnal form of the suffering is often alleviated by protecting the teeth with a splint.
U.S. Pat. No. 4,669,477 discloses an apparatus for treatment of bruxism. This apparatus is based on that the muscle activity in the jaw muscles of a patient can be sensed and compared with a threshold value that may be adjusted. If the sensed muscle activity exceeds the threshold value a stimulation signal is generated. The stimulation signal is applied to the jaw muscle by means of electrodes. In an embodiment of this apparatus the stimulation signal comprises a start region, where the intensity of the signal may be increased gradually, a stimulation region where the intensity is constant, and a termination region where the intensity of the signal decreases gradually.
It is however a problem that the apparatus uncritically triggers a stimulation when the threshold value is exceeded. It turns out that long time use of the apparatus has a preventive effect and that bruxism thus may be avoided without using the apparatus. The patient learns unconsciously that he/she must not grind the teeth. This is primarily caused by that when using the apparatus the patient is punished with small electric shocks in the form of the stimulation signal when the muscle activity exceeds the threshold value. Since a typical person that may or may not suffer from bruxism has a considerable muscle activity in the jaw region caused by dreaming, which activity may have the same level as real bruxism, a considerable number of stimulations of the jaw muscle will be triggered during normal sleep when the apparatus is used. With reference to the above-mentioned effect that the patient learns from the punishment he/she receives in the form of small electric shocks there is a considerable danger that the patient similarly is punished for the normal and natural jaw activity that takes place during sleep. This natural jaw activity may prove to be important for the dreams a person has during sleep.
From U.S. Pat. No. 6,093,158 A there is further known a system for treatment of inter alia bruxism. This document describes an apparatus that may be wholly inserted in the ear canal in the same manner as an hearing aid (ITE heraring aid) and where by means of a microphone sounds may be picked-up in the ear, which sounds may possibly stem from teeth grinding. By means of a processor it is investigated whether criteria for detection of bruxism are fulfilled where after a sound signal may be transmitted by means of a transducer as a stimulation to the user.
The criteria for detection of bruxism may be exceeding of a sound level that can be adjusted by the user. Other criteria such as the number of events pr. unit of time and the duration are generally mentioned. Besides from this the signal processing itself is not further described. The document mentions various options regarding detection, e.g. by means of sound sensors, microphones, EMG (Electromyographic) electrodes etc. and feedback options, for example with sound.
In an embodiment the apparatus may detect small changes in the structure of an ear by means of a transmitter and a receiver for example if the user begins grinding of the teeth. This embodiment has the flaw that the changes may possibly be quite normal jaw movements that may not be synonymous with teeth grinding. The apparatus may therefore perceive these muscle activities as undesired muscle contractions in the form of teeth grinding and thus activate the feedback
In another embodiment the sound is measured in the ear, which sound may stem from grinding or snoring. No criteria are mentioned for how these sound signals/sources are differentiated from each other. This prior art system functions in the manner that a threshold value is adjusted and if this threshold value is exceeded the feedback will be activated. This means that if the user for example coughs, talks in his/her sleep or generates a normal sound during sleep, this will cause an exceeding of the threshold value and thus the patient will receive an undesired feedback.
Further an embodiment comprises additional sound sensors that may be placed at various locations on the face. If the microphone placed in the ear cannot detect the sound via the ear canal these sensors will be able to detect the sound that may inter alia stem from teeth grinding or snoring. Hereby the disadvantage will again arise that the sound source can be anything that uncritically will activate the feedback if the threshold value is exceeded.
In this prior art document it is also mentioned that e.g. other types of sensors may be placed in the mouth of the user. A sound source for use as feedback may also be placed on the body of the user or at the side of the bed. The feedback may possibly be activated in the form of a vibrator placed on a location on the body.
In the document it is thus mentioned that a stimulation feedback may be used but no explanation has been given as to how such a stimulation is activated and which criteria must be fulfilled besides exceeding of the threshold value. It is thus not explained which properties the stimulation should have.
As mentioned this known system will have the drawback that normal bite-activities, sounds, movements etc. during sleep may cause an activation of the feedback, since steps have not been taken to differentiate between these. Further, considerations have not been taken as regards the influence via the sensors from other external sources. It is thus also a general drawback that the apparatus will uncritically trigger a feedback when the threshold value is exceeded.
Finally it may be mentioned that in regard to such a prior art apparatus there will be a risk that the user is wakened during sleep, inter alia caused by feedback in situations that are not related to bruxism. This may have the disadvantage that the sleep rhythm is disturbed which will stress the user further, which again may worsen the bruxism of the user, since stress is an essential cause of bruxism.
It is thus an objective of the invention to provide an apparatus for and a method of monitoring of bruxism, by means of which these drawbacks are alleviated.
It is thus in particular an objective of the invention to provide such an apparatus and such a method, by means which an individual adaptation to the user may be achieved.
Further, it is an objective of the invention to provide such an apparatus and such a method by means of which considerations may be taken in regard to normal movements and/or sounds made during sleep that the user does not have to be “punished” for, i.e. meaning that no feedback signal will be emitted in such situations.
Additionally it is an objective of the invention to provide such an apparatus and such a method whereby it is seen to it that the user should not be awakened when the feedback is activated as a sound or a vibration etc.
It is even further an objective of the invention to provide such apparatuses and such methods that will reduce or even prevent the disadvantage that the sleep rhythm of the user is disturbed because of erroneously triggered feedback signals, whereby the sleep rhythm of the user as far as possible will not be disturbed.
Finally it is an objective of the invention to provide an apparatus for and a method of monitoring of muscle activities that may be used not only for monitoring with a view to detection of bruxism but also in a variety of other situations where it is desirable to be able to detect inopportune or of other reasons undesired muscle activities, whereby the attention of an individual may be brought to this by means of a feedback signal.
These and other objectives are achieved by the invention as explained in further detail in the following.